Functional characterization of two novel non-synonymous alterations in CD46 and a Q950H change in factor H found in atypical hemolytic uremic syndrome patients.

Atypical hemolytic uremic syndrome (aHUS) is a disease of complement dysregulation, characterized by hemolytic anemia, thrombocytopenia and acute renal failure. Mutations in complement inhibitors are major risk factors for development of aHUS. The three aHUS patients reported in this study had several previously identified alterations in complement inhibitors; e.g. risk haplotypes in CD46 and factor H but we also identified two novel heterozygous non-synonymous CD46 alterations (p.E142Q and p.G259V). Presence of G259V caused decreased expression of the recombinant mutant CD46 compared to wild type (WT). Western blot analysis showed that the majority of the expressed G259V protein was in the precursor form, suggesting that it is processed less efficiently than WT. Low CD46 expression on the surface of the patient's neutrophils confirmed the in vitro results. Further, G259V had a substantially impaired ability to act as a cofactor to factor I, in the degradation of both C3b and C4b. The E142Q mutant showed neither decreased expression nor impaired function. Two of the patients also had a heterozygous non-synonymous alteration in factor H (p.Q950H), reported previously in aHUS but not functionally tested. This variant showed moderately impaired function in hemolytic assays, both using patient sera and recombinant proteins. The recombinant Q950H also showed a somewhat decreased expression compared to WT but the complement inhibitory function in fluid phase was normal. Taken together, we report a novel CD46 alteration showing both a decreased protein expression and substantially impaired cofactor function (G259V) and another without an effect on expression or cofactor function (E142Q). Moreover, mild consequences of a previously reported aHUS associated rare variant in factor H (Q950H) was also revealed, underlining the clear need for functional characterization of each new aHUS associated mutation.

[The benefit of plasmapheresis in a patient with steroid-resistant nephrotic syndrome and anuria--long-term follow-up]. / Povoljan efekat plazmafereze kod bolesnika sa steroid-rezistentnim nefrotskim sindromom i anurijom--dugotrajno nadgledanje.

Recently, plasma exchange (PE) has been added to the treatment regimen for patients with steroid-, cyclophosphamide-, and cyclosporine-resistant nephrotic syndrome. This is a case report of a female patient with severe acute renal failure (ARF) during the relapse of steroid-resistant nephrotic syndrome (SRNS) who recovered completely after PE and became steroid-sensitive in further follow-up of 48 months. An 8-year-old girl was referred to Nephrology Department of the University Children's Hospital due to relapse of SRNS complicated with ARF. Her nephrotic syndrome (mesangioproliferative glomerulonephritis) was diagnosed at the age of 17 months. During the following 6 years, she was given several therapeutic regimens including pulse prednisolone, cyclophosphamide, Cyclosporine (CyA), but she continued to have frequent relapses and during the last six months she was steroid- and cyclosporine-resistant. Three days before admission, she was febrile, had cellulites of the lower abdominal wall, diarrhea, vomiting, hypovolemic shock with generalized edema, severe hypoproteinemia and hypoalbuminemia. In a local hospital, she was treated with fresh frozen plasma, albumin, methylprednisolone, furosemide and antibiotics, but she became anuric and was referred to our hospital. There were no signs of hemolysis. Anuria lasted for 12 days. She was discharged after 42 days in remission with normal GFR. Principal treatment included: 13 sequential hemodialysis sessions (30% of body weight was removed as excess volume), 6 PE, corticosteroids, CyA, ACE inhibitor, antibiotics, antimycotics, and cimetidine. Six PE sessions were performed every other day. In further 48-month follow-up, while under the treatment of CyA the patient had a few steroid-sensitive relapses, the first being 6 months after PE. The second kidney biopsy showed focal segmental glomerulosclerosis with no signs of apparent CyA nephrotoxicity. "Malignant" course of disease in our patient was a good reason to introduce PE into the treatment. Since PE was the only additional mode of treatment, it is believed that its effect was crucial for milder activity of the disease.